In general, electric power supply systems that supply electric power to a load provided in a rotating member that is rotatable in relation to a fixed member can be broadly classified into a contact-type electric power supply system in which an electrode is brought into contact from outside with an electrode provided in a rotating member in an exposed manner to supply electric power to the electrode and a non-contact-type electric power supply system in which electric power is supplied to an electrode provided in a rotating member in a non-exposed manner without making contact with the electrode.
Among these electric power supply systems, a conventional contact-type electric power supply system is disclosed in Patent Document 1, for example. In this system, an electrode called a slip ring is provided in a rotating member, an electrode called a brush is provided outside the rotating member, and the slip ring and the brush make sliding-contact with each other whereby electric power is transmitted.    Patent Document 1: Japanese Unexamined Patent Application, Publication No. H06-282801